The present invention relates generally to an aluminum alloy suitable for elevated temperature applications.
Gas turbine engines are commonly made of titanium-, iron- cobalt- and nickel-based alloys. During use, many components of the gas turbine engines are commonly subject to elevated temperatures. Lightweight metals, such as aluminum and magnesium, are often used for some components to enhance performance and reduce the weight of engine components. A drawback to employing conventional aluminum alloys is that the strength of many such alloys drops rapidly at temperatures above 150° C., making these alloys unsuitable for certain elevated temperature applications.
Precipitation strengthening is commonly employed to strengthen aluminum alloys. After a primary alloy system, that is either a binary or ternary eutectic, is cast and solidified, it is heat treated at around 500° C. to solution the alloy and optimally arrange the primary alloy elements, such as copper, silicon, and zinc. Rare earth elements are often used as minor alloy elements, typically in quantities of less than 1% by weight. After casting, the aluminum alloy is quenched in water to maintain the alloy elements as a supersaturated solution in the solid aluminum matrix. The aluminum alloy is aged by reheating at appropriate temperatures for various times, e.g., to 160° to 180° C. for 10 to 12 hours, and the elements in the supersaturated solution slowly precipitate out of the aluminum matrix to form fine particles that strengthen the aluminum alloy. The cast shape may then be finished with a machining operation.
There are several drawbacks to prior precipitation strengthening methods used to form an aluminum alloy. For one, the precipitated alloy particles grow at temperatures over 150° C., reducing both the number of alloy particles and the strength of the aluminum alloy. Intermetallic dispersion strengthening overcomes this deficiency by making use of thermally stable particles. However, to achieve an equivalent strengthening effect at ambient temperature, it requires rapid solidification, increasing the processing cost of the aluminum alloy. In previous aluminum alloys, a fine and uniform microstructure is only achievable with slow cooling rates when the system is eutectic and by precipitation and fast cooling.
Hence, there is a need in the art for an improved aluminum alloy that retains strength at elevated temperatures, can be produced by conventional casting methods, and overcomes the other problems of the prior art.